For example, JPH10-231946A teaches a spring load adjusting apparatus that requires sealing between a sleeve (serving as a female-threaded member) and an adjust screw and is provided in a spool valve.
The technique of JPH10-231946A will now be described with reference to FIG. 10. The spring load adjusting apparatus of FIG. 10 includes the sleeve 102, which serves as the female-threaded member. A cylindrical hole J1, which forms a cylindrical inner peripheral wall, extends in the sleeve 102 in an axial direction. The adjust screw 104 has a cylindrical tubular portion J2. The cylindrical tubular portion J2 is inserted into the cylindrical hole J1 and seals between the cylindrical hole J1 and the cylindrical tubular portion J2.
In JPH10-231946A, the adjust screw 104 needs to be arranged such that the adjust screw 104 is threadably rotatable relative to the sleeve 102. Therefore, an annular clearance C needs to be formed between the cylindrical hole J1 and the cylindrical tubular portion J2.
Furthermore, according to JPH10-231946A, the required sealing is achieved between the cylindrical hole J1 and the cylindrical tubular portion J2. Therefore, the annular clearance C between the cylindrical hole J1 and the cylindrical tubular portion J2 needs to be very small.
Thus, both of the sleeve 102 and the adjust screw 104 need to be processed with high accuracy (high processing precision), and this requirement will result in an increase in the costs of the spring load adjusting apparatus and thereby the costs of the spool valve.
Furthermore, the technique of JPH10-231946A provides the required sealing between the cylindrical hole J1 and the cylindrical tubular portion J2. In order to provide the required sealing between the cylindrical hole J1 and the cylindrical tubular portion J2, a seal length L (an axial extent of an overlapped area between the cylindrical hole J1 and the cylindrical tubular portion J2) needs to be increased.
Therefore, the axial size of the spring load adjusting apparatus is disadvantageously increased, and thereby a size of the spool valve, which has the spring load adjusting apparatus, is disadvantageously increased.